1. Field of the Invention
This invention relates to a blowhole.sup.. pit preventing agent and an arc-welding method using the same, and more particularly to an effective means for preventing the occurrence of blowhole and pit as a serious defect in the arc-welding of galvanized sheets.
2. Relates Art Statement
In general, surface treated materials obtained by applying zinc or zinc alloy or a composition containing them to a surface of a metallic substrate to form a plated film or coated film are called as a galvanized sheet inclusive of zinc-plated steel sheet. When the treated surfaces of the galvanized sheets are lapped one upon the other to form a lap joint by welding, zinc or the like is vaporized by a welding heat to produce a high vapor pressure of zinc in the joint face, whereby blowholes or pits are frequently produced in weld bead. This becomes a serious problem up to the present, and consequently it is unable to apply the arc welded joint of the galvanized sheet to portions requiring severer quality of welded joint, for example, high-strength members and the like.
Prior to the welding, zinc or the like in the vicinity of the welded joint portion was previously removed by a mechanical means, or by vaporization through a gas burner or an ahead torch, or by a chemical means such as use of a remover or the like. In this case, not only the number of steps undesirably increases but also zinc or the like existent in the portion other than the welded portion is unnecessarily removed or the portion near to the welded portion is damaged to undesirably injure the rust preventing ability and appearance of base metal.
Since the remover contains a large amount of organic solvent, acid, alkali or the like, the use of such a remover unfavorably damages the working environment and safety.